Copper extraction with either salicylaldoximes or benzophenone oximes and alkylphenols

ABSTRACT

A process for extracting metal values from aqueous solutions of metal salts which comprises the steps of contacting the aqueous solution with a solution in a water-immiscible organic solvent of one or more o-hydroxyaryloximes containing at least 3 aliphatic or alicyclic carbon atoms and which are strong metal extractants and one or more alkylphenols optionally containing one chlorine atom or one cyano group, separating from the aqueous phase the solvent phase containing metal in the form of a complex with the o-hydroxyaryloxime contacting the solvent phase with an aqueous mineral acid, and separating the solvent phase from the aqueous phase containing metal in the form of a salt with the mineral acid.

This is a continuation of application Ser. No. 965,498 filed Dec. 1,1978, now U.S. Pat. No. 4,231,888 which is a division of Ser. No.756,067, filed Jan. 3, 1977, now U.S. Pat. No. 4,142,952.

This invention relates to an improvement in the process for extractingmetals from aqueous solutions, especially solutions obtained by leachingores with acids, using o-hydroxyaryloximes as extracting agents.

It is known to extract metals, especially copper, from aqueous solutionscontaining the metal in the form of, for example, a salt by contactingthe aqueous solution with a solution of an o-hydroxyaryloxime in awater-immiscible organic solvent and then separating the solvent phaseloaded with metal, i.e. containing a part of the metal in the form of achelate compound with the o-hydroxyaryloxime. The metal can then berecovered from the metal loaded solvent phase by stripping with acidsolutions followed, for example, by electrowinning.

The reaction leading to the metal chelate compound also forms acid andcauses a lowering of the pH. This reaction is reversible and proceeds toan equilibrium point which will favour formation of the chelate compoundas the pH is increased. The metal salt-containing aqueous solutions fromwhich metal e.g. copper is to be extracted will frequently be leachliquors obtained by extracting metal ores with acid and will in somecases have a low pH. Since the amount of chelate compound formed atequilibrium is lower as the pH is decreased only thoseo-hydroxyaryloximes which have a strong chelating power will be able toachieve a high degree of extraction from those aqueous leach liquorshaving very low pH or high copper content.

The advantage of high copper extraction shown by these stronglychelating oximes is to some extent offset by the large amount of copperwhich remains as chelate in the solvent after stripping with acid ofconvenient strength. While this residual copper as chelate is not lostsince it can be recycled to the extraction stage, a reduction in theamount of residual copper chelate would, in the absence of anycomparable reduction in the degree of copper extraction from the aqueoussolution, afford an improvement in the overall efficiency of theprocess. It has now been found that the amount of copper removed inthese cases from the solvent phase in the stripping stage issignificantly increased if the solvent phase contains a phenol of acertain type.

According to the invention there is provided a process for extractingmetal values from aqueous solutions of metal salts which comprises thesteps of contacting the aqueous solution with a solution in awater-immiscible organic solvent of one or more o-hydroxyaryloximescontaining at least 3 aliphatic or alicyclic carbon atoms and which arestrong metal extractants as hereinafter defined and one or morealkylphenols optionally containing one chlorine atom or cyano group,separating from the aqueous phase the solvent phase containing metal inthe form of a complex with the o-hydroxyaryloxime, contacting thesolvent phase with an aqueous mineral acid, and separating the solventphase from the aqueous phase containing metal in the form of a salt withthe mineral acid.

o-Hydroxyaryloximes generally of value for extracting metal values fromaqueous solutions of metal salts are well known and include for examplealkyl or alkoxysalicylaldoximes as described in Belgian Patent Nos.796,835 and 833,774, substituted, e.g. by alkyl or alkoxy groups,o-hydroxyaryl alkyl ketoximes as described in Specifications No.1322532, German Offenlegungsschrift No. 2407200 and Belgian Patent No.804,031, o-hydroxyaryl benzyl ketoximes as described in Belgian PatentNo. 804030, and o-hydroxybenzophenone oximes as described in U.S. Pat.Nos. 3,428,449 and 3,655,347. In order to confer adequate solubility ofthe oxime and its metal derivative in the organic solvents the oximesshould contain groups, e.g. alkyl, alkylene or cycloalkyl groupscontaining at least three carbon atoms and preferably not more than 20carbon atoms. The solubility is generally further enhanced by the use ofmixtures of oximes.

Of the above o-hydroxyaryloximes only those which are strong metalextractants are useful in the process of the invention. Theseo-hydroxyaryloximes are defined on those which in 0.2 molar solution inan aliphatic hydrocarbon solution when loaded with 50% of thetheoretical uptake of copper will be in equilibrium with a 0.1 molarsolution of copper as copper perchlorate at a pH less than 1.

As examples of o-hydroxyaryloximes which are strong metal extractantsthere may be mentioned o-hydroxyaryl ketoximes containing electronwithdrawing substituents in the 3-position such as3-chloro-5-nonylbenzophenone oxime and similar compounds disclosed inU.S. Pat. No. 3,655,347, which in the test for strength given abovewould be in equilibrium at a pH less than 0.5, o-hydroxyaryl ketoximescontaining electron withdrawing substituents such as halogensubstituents in the 3-position as disclosed in Specification No.1,322,532 or in Belgian Patents Nos. 804030 and 804031, and substitutedsalicylaldoximes such as alkylsalicylaldoximes described in BelgianPatents Nos. 796835 and 833774, which in the above test for strengthwould be in equilibrium at about pH 0.5.

In contrast o-hydroxyaryl ketoximes which are devoid of electronwithdrawing substituents in the 3-position, examples which are describedin Specification 1322532, U.S. Pat. No. 3,428,449 and Belgian PatentsNos. 804030 and 804031, in the above test are usually in equilibrium atpH about 1.2 or higher and are not suitable for use in the presentinvention. The addition of alkyl phenols does improve slightly the metaltransfer from these compounds at the strip stage but this advantage ismore than counterbalanced by a considerable decrease in the amount ofmetal transferred to the oxime at the extraction stage and the overalleffect is adverse. In the case of the oximes which are strong metalextractants the addition of alkyl phenols as in the process of theinvention leads to some decrease in metal transfers at the extractionstage but this disadvantage is materially less than the advantageobtained in increased metal transfer at the strip stage and the overallresult of adding the alkylphenol is beneficial.

Particularly useful, owing to their ability to deal with aqueoussolutions containing high copper concentrations and their rapid rates ofmetal transfer, are the alkyl salicylaldoximes especially wherein thealkyl groups are branched chain alkyl groups containing at least fivecarbon atoms and mixtures of these, for example mixed5-nonylsalicylaldoximes and mixed 5-heptylsalicylaldoximes, andparticularly mixtures of 5-nonylsalicylaldoximes, in which thecomponents of the mixture differ in configuration of the branched chainnonyl group, derived by formylation and oximation from the mixedp-nonylphenols obtained by condensation of phenol with propylene trimer,and mixtures of 5-heptylsalicylaldoximes, in which the components of themixture differ in configuration of the heptyl group, similarly derivedfrom phenol-heptylene condensate.

As alkylphenols there may be mentioned any cresol and mixtures of theseand especially phenols containing from 3 to 15 alkyl carbon atoms, forexample p-tert-butylphenol, p-heptylphenol, 4-amyl-5-methylphenol,2-chloro-4-nonylphenol, 2-cyano-4-nonylphenol, p-dodecylphenol,m-pentadecylphenol and p-nonylphenol and mixtures of these. Phenolshaving alkyl groups containing more than 15 carbon atoms are notpreferred as they tend to cause emulsification. The preferred phenolscontain alkyl groups having from 4 to 12 carbon atoms, especially themixed p-nonylphenols obtained by condensation of phenol and propylenetrimer.

The amount of oxime used will depend upon the concentration of metalsalt in the aqueous solution and the plant design. It is preferredhowever to use from 5 g. to 200 g. of oxime per liter of organicsolution. Higher concentrations afford organic phases of too highviscosity for convenient handling and lower concentrations involve theuse of unnecessarily large volumes of solvent.

For use with aqueous solutions containing 5 g. or more per liter ofmetal such as copper it is preferred to use 20 to 200 g. of oxime perliter of organic solution in conjunction with an amount of alkylphenolsuitably from 10% to 300% of the weight of the oxime, and especiallyfrom 30% to 200%. The effect of the phenol is more marked the higher theconcentration of oxime and comparatively lower proportions of of thealkylphenol with respect to the oxime are required to bring about asatisfactory improvement in strip efficiency when operating at highconcentrations.

For use with more dilute solutions containing, for example, from 0.5 to3 g. of metal per liter, oxime solutions containing from 5, and moreparticularly 10, to 20 g of oxime per liter are preferably used, theamount of alkylphenol being preferably from 2 to 10 times the weight ofoxime although higher amounts, such as 20 times, may be used if desired.

The process may be applied to the extraction of any metal capable offorming a lyophilic complex with the oxime, for example cobalt, nickel,vanadium, chromium, zinc, tin, cadmium, gold, silver, mercury and,especially, copper.

The first and second steps of the process may conveniently be carriedout by bringing together the aqueous solution and the solution of theoxime in the organic solvent at a suitable temperature, usually ambienttemperature, although somewhat higher temperatures may be used ifoperationally convenient, agitating or otherwise disturbing the mixtureof liquids so that the area of the water-solvent interfacial layer isincreased in order to promote complex formation and extraction, and thendecreasing the agitation or disturbance so that the aqueous and solventlayers settle and can be conveniently separated. The process may becarried out in a batchwise manner or preferably continuously.

The amount of organic solvent to be used may be chosen to suit thevolume of aqueous solution to be extracted, the concentration of metals,and the plant available to carry out the process. It is preferred,especially when operating the process continuously, to bring togetherapproximately equal volumes of the organic solution and the aqueoussolution.

The conditions, particularly pH, under which first and second steps ofthe process are carried out are chosen to suit the metal or metalspresent in the aqueous solution. It is generally desirable that underthe chosen conditions any other metals present should not form stablecomplex compounds with the oxime in order that substantially only thedesired metal is extracted from the aqueous solution. Since formation ofthe complex compound may involve the liberation of acid, it may benecessary to add e.g. alkali during the process to maintain the pHwithin the desired range in which the metal complex is stable but it isgenerally preferable to avoid this, especially in acontinuously-operated process. The process of the invention isespecially suitable for use with copper since this metal forms a complexwith o-hydroxyaryloximes which is stable at low pH values and byoperating at pH below 3 copper can be extracted substantially free fromiron, cobalt and nickel.

As organic solvents there may be used any mobile organic solvent ormixture of solvents which is immiscible with water and, under the pHconditions used, inert to water, to the metal, and to the oxime,especially aliphatic, alicyclic and aromatic hydrocarbons and mixturesof any of these particularly mixtures which have little or no aromatichydrocarbon component, and halogenated particularly chlorinatedhydrocarbons including, as solvents more dense than water, highlyhalogenated hydrocarbons such as perchloroethylene, trichloroethane,trichloroethylene and chloroform.

The third and fourth steps of the process may conveniently be carriedout by bringing together the metal-bearing solution of the oxime in theorganic solvent, obtained from the second stage of the process, and anaqueous solution of a mineral acid at a suitable temperature, usuallyambient temperature, although somewhat higher temperatures may be usedif operationally convenient, agitating or otherwise disturbing themixture of liquids so that the area of the aqueous-solvent interfaciallayer is increased in order to promote decomposition of the complex andrecovery of the metal and then decreasing the agitation or disturbanceso that the aqueous and solvent layer settle and then separating thelayers. Suitable relative volumes of aqueous and organic phase are thoseconventionally used in metal extraction processes for example 1:1. Theprocess may be carried out in a batchwise manner or preferablycontinuously. The stripped organic layer, containing regenerated oxime,alkylphenol and some residual copper may be re-used in the first step ofthe process. The aqueous layer containing metal salt may be treated inany conventional manner, especially by electrolysis, to provide themetal.

The mineral acid is preferably sulphuric acid, suitable strengths beingfrom 100 to 250 g. per liter. After removal of a convenient part of themetal by electrolysis the recovered aqueous acid, containing residualmetal salt, may be re-used in the third step of the process.

If desired, other ligands may be used, in addition to the oximes andother compounds, such as conditions, for example long chain aliphaticalcohols such as capryl alcohol, isodecanol, tridecyl alcohol or2-ethylhexanol, may also be present, suitably in amounts of from 0.5 to10% by weight of the organic solvent.

The addition of anionic surface active agents such as organic sulphonicacids or acid phosphoric esters is sometimes desirable in order toincrease the rate of complex formation and transfer of metal valuesbetween the aqueous and organic phases.

Mixtures of o-hydroxyaryloximes and alkylphenols, obtained for exampleby admixture of the components in any convenient manner, suitable foruse in the process of the invention when dissolved in water-immiscibleorganic solvents, and solutions of such mixtures in water-immiscibleorganic solvents are also features of the invention. Such solutions maybe of suitable strength for use in the process of the invention or, forconvenience, for storage or transport, may be more concentrated andrequire dilution before use.

The invention is illustrated but not limited by the following Examplesin which all parts and percentages are by weight unless otherwisespecified.

EXAMPLE 1

20 Parts of a solution containing 200 g. per liter of5-nonylsalicyaldoxime (prepared as described in Belgian Patent No.796,835) in Escaid 100 (an 80% aliphatic kerosene-type solvent) wasstirred vigorously at 20° C. with 40 parts of an aqueous solutioncontaining 15 g. per liter of copper as copper sulphate and sulphuricacid to bring the pH to 2.0. After 15 minutes the stirring was stopped,the phases allowed to settle and the solvent phase removed and analysedfor copper.

15 parts of the solvent phase were then stirred vigorously for 15minutes with 50 parts of an aqueous strip solution containing 30 g. perliter of copper as sulphate and 150 g. per liter of sulphuric acid. Thephases were allowed to settle and the organic phase analysed for copper.

The results showed that the solvent phase after the extraction stagecontained 22.02 g. per liter of copper and after stripping contained15.60 g. per liter of copper indicating a recovery of copper of 6.42 g.per liter of oxime solution used.

To demonstrate the improvement obtained by the process of the inventionthe above procedure was repeated using an Escaid solution containingalso 100 g per liter of p-nonylphenol.

The solvent phase after extraction contained 21.10 g per liter of copperand after strip 10.99 g. per liter of copper indicating a recovery ofcopper of 10.11 g. per liter of oxime solution, and an increase of 57%in the amount of copper recovered per liter of oxime solution used.

EXAMPLE 2

The procedure of Example 1 was repeated using in the extraction stage 1part of an Escaid 100 solution containing 50 g per liter of5-nonylsalicylaldoxime and, when appropriate, 50 g per liter ofp-nonylphenol and 2 parts of an aqueous solution at pH 2.0 containing3.0 g per liter of copper, and in the strip stage 1 part of the loadedorganic phase and 1 part of the strip solution used in Example 1.

The results were as follows:

In absence of nonylphenol the solvent phase contained 5.34 g. per literof copper after extraction and 3.40 g. per liter after strip, indicating1.94 g. per liter recovery of copper.

In presence of nonylphenol the copper contents were 5.00 and 2.26 g perliter respectively, indicating a copper recovery of 2.74 g. per liter,this being an increase of 41% over the recovery in absence ofnonylphenol.

EXAMPLE 3

The procedure of Example 2 was repeated replacing the5-nonylsalicylaldoxime with 64.4 g. per liter (a corresponding molarquantity) of 5-nonyl-2-hydroxy-benzophenone oxime (U.S. Pat. No.3,428,449).

The results were as follows:

In absence of nonylphenol the solvent phase contained 4.00 g per literof copper after extraction and 0.28 g. per liter after strip, indicatinga copper recovery of 3.72 g. per liter.

In presence of nonylphenol the copper contents were 3.52 and 0.14 g perliter respectively, indicating a copper recovery of 3.38 g per liter,and demonstrating that with this ketoxime the addition of nonylphenolhas an adverse effect.

EXAMPLE 4

The procedure of Example 2 was repeated replacing the5-nonylsalicylaldoxime with 71 g per liter (a corresponding molarquantity), of 2-hydroxy-3-chloro-5-nonylbenzophenone oxime (U.S. Pat.No. 3,655,347).

The results were as follows:

In absence of nonylphenol the solvent phase contained 4.80 g. per literof copper after extraction and 4.04 g per liter after strip, indicatinga copper recovery of 0.76 g. per liter.

In presence of nonylphenol the copper contents were 4.73 and 3.745 g.per liter respectively indicating a copper recovery of 0.985 g perliter.

2-hydroxy-3-chloro-5-nonylbenzophenone oxime is a strong metalextractant as defined hereinbefore and these results demonstrate thatwith this ketoxime the addition of nonylphenol has a beneficial effectof increasing the copper recovery under the above conditions by 30%.

EXAMPLE 5

Solutions of Escaid 100 were prepared containing 50 g. per liter of5-nonylsalicylaldoxime and amounts (equimolar) of alkylphenol as listedbelow. The solutions were each contacted with aqueous copper sulphatesolutions until loaded with 5.4 g. per liter of copper. 1 part of eachof the loaded solutions were then stirred vigorously until equilibriumhad been established with 0.25 parts of the aqueous strip solution usedin Example 1, and the solvent phase then separated and analysed forcopper content.

The results were as follows:

    ______________________________________                                                      Concentration                                                                             Copper content of                                                 of phenol   stripped solvent phase                              Phenol        (g. per liter)                                                                            (g. per liter)                                      ______________________________________                                        none          --          3.59                                                m-pentadecylphenol                                                                          57.8        2.92                                                2-methyl-4-nonylphenol                                                                      44.5        3.15                                                p-tert-butylphenol                                                                          28.5        2.94                                                2-chloro-4-nonylphenol                                                                      48.3        2.81                                                p-nonyl phenol                                                                              41.8        2.84                                                ______________________________________                                    

EXAMPLE 6

An extractant solution was prepared containing 15 g. of5-nonylsalicylaldoxime (prepared as described in Belgian Patent No.796,835) and 45 g. of 4-nonylphenol per liter in Escaid 100 (an 80%aliphatic kerosene type solvent). 30 Parts by volume of this solutionwere contacted by vigorous stirring for 15 minutes at 25° C. with 60parts of an aqueous solution containing 1.0 g. per liter of copper asthe sulphate at pH 2.0 so as to establish an equilibrium distribution ofthe copper between both phases. The phases were allowed to settle andthe organic phase analysed for copper.

Part of the copper containing solvent phase was then `stripped` byvigorous stirring with an equal volume of an aqueous solution containing150 g. per liter of sulphuric acid and 30 g. per liter of copper assulphate, such a solution being typical of the spent electrolyte from anelectrolytic process for the final recovery of copper. The phases wereallowed to settle and the organic phase analysed for copper.

The solvent phase after extraction contained 1.49 g. per liter of copperand after stripping contained 0.42 g. per liter of copper, indicating arecovery of copper of 1.07 g. per liter of oxime/nonylphenol extractantsolution.

To demonstrate the improvement obtained by the process of the inventiondescribed, the above procedure was repeated using an Escaid 100 solutioncontaining 15 g. per liter of 5-nonylsalicylaldoxime, but nononylphenol. Under these conditions the solvent phase was found tocontain 1.58 g. per liter of copper after the extraction stage, and 0.78g. per liter of copper after the strip stage, giving a copper recoveryof only 0.80 g. per liter of oxime solution.

EXAMPLE 7

Various volume ratios of an extractant solution containing 15 g. perliter of 5-nonylsalicylaldoxime and 45 g. per liter of 4-nonylphenol inEscaid 100, and an aqueous solution containing 1.0 g. per liter ofcopper as sulphate at pH 2.0 were equilibrated by vigorous stirring for15 minutes at 25° C. The phases were allowed to settle and each analysedfor copper to give the copper distribution. The results were as follows:

    ______________________________________                                        Ratio of Ex-                                                                           3:1    2:1    1:1  1:1.5                                                                              1:2  1:3  1:4  1:6                           tract/Aque-                                                                   ous volumes                                                                   Copper in                                                                              0.34   0.50   0.98 1.33 1.49 1.59 1.64 1.65                          Organic                                                                       phase g/l.                                                                    Copper in                                                                              --     --     0.04 0.13 0.26 0.47 0.59 0.73                          aqueous                                                                       phase g/l.                                                                    ______________________________________                                    

EXAMPLE 8

An extractant solution prepared as in Example 7 was contacted with anaqueous copper solution until loaded to 1.77 g. per liter of copper.Portions of this loaded solution were then vigorously stirred at variousvolume ratios with an aqueous strip solution containing 150 g. per literof sulphuric acid and 30 g. per liter of copper as sulphate, toestablish equilibrium. The phases were allowed to settle and eachanalysed for copper content. The results were as follows:

    ______________________________________                                        Ratio of Extractant/                                                                      1:1    2:1    3:1  5:1  7:1  9:1  15:1                            strip solution                                                                volumes                                                                       Copper in Organic                                                                         0.42   0.44   0.46 0.49 0.53 0.56 0.62                            phase g/l.                                                                    Copper in Aqueous                                                                         31.5   32.9   34.2 36.7 39.0 41.8 46.8                            phase g/l.                                                                    ______________________________________                                    

EXAMPLE 9

One part by volume of an Escaid 100 solution containing 50 g per literof 5-nonylsalicylaldoxime and 50 g per liter of p-cresol was stirredvigorously with two parts of an aqueous solution containing 3.0 g perliter of copper as the sulphate at pH 2.0. After 15 minutes the stirringwas stopped, the two phases allowed to separate and the organic phaseremoved and analysed for copper.

One part of the copper loaded organic phase from the above experimentwas then contacted with two parts by volume of an aqueous acid stripsolution containing 150 g per liter of sulphuric acid and 30 g per literof copper as the sulphate. After 15 minutes the stirring was stopped,the phases allowed to separate, and again a portion of the organic phaseanalysed for copper.

The copper contents of the loaded and stripped organic solutions were5.29 and 2.34 g per liter respectively indicating a copper transfer bythe reagent of 2.95 g per liter. In the absence of p-cresol the loadedsolvent phase contained 5.34 g per liter of copper, and after stripping3.40 g per liter indicating a copper transfer of only 1.94 g per liter.The addition of p-cresol has made an improvement in the copper transferof 52%.

EXAMPLE 10

The procedure of Example 9 was repeated replacing the p-cresol by2-cyano-4-nonylphenol. The results were as follows:

Copper in loaded organic phase=4.37 g per liter

Copper in stripped organic phase=1.79 g per liter

Copper transferred by extractant solution=2.58 g per liter

This is an improvement in the amount of copper transferred of 43%compared to that when no phenolic compound is added.

EXAMPLE 11

The procedure of Example 2 was repeated but replacing the5-nonylsalicylaldoxime by 5-heptylsalicylaldoxime. The results were asfollows:

5.55 g per liter of copper after the extraction stage, and

3.80 g per liter after the strip stage, indicating a recovery of

1.75 g per liter of copper.

In presence of nonylphenol the solvent phase contained

5.27 g per liter of copper after extraction, and

2.64 g per liter of copper after strip, indicating a copper recovery of

2.63 g per liter, this being an increase of 50% over the recovery inabsence of nonylphenol.

I claim:
 1. A process for extracting copper values from aqueoussolutions of copper salts which comprises the steps of (a) contactingthe aqueous solution with a solution in a water-immiscible, organicsolvent of (1) o-hydroxyaryloximes selected from the group consisting ofa mixture of 5-nonylsalicylaldoximes, a mixture of5-heptylsalicylaldoximes and a mixture of2-hydroxy-3-chloro-5-nonylbenzophenone oximes and (2) an alkylphenolcontaining from 3 to 15 alkyl carbon atoms, (b) separating from theaqueous phase the solvent phase containing copper in the form of acomplex with the indicated o-hydroxyaryloxime, (c) contacting thesolvent phase with an aqueous mineral acid, and (d) separating thesolvent phase from the aqueous phase containing copper in the form of asalt with the mineral acid, the amount of (2) in said solvent being inthe range of 0.1 to 20 times the weight of (1) and such that with theother conditions used, the overall copper recovery resulting from steps(a) to (d) is greater than when (2) is not included, the pH during thecontacting step (a) being such that the complex which is formed isstable.
 2. A process according to claim 1 wherein the alkyl phenolcontains one chlorine atom or cyano group.
 3. A process as claimed inclaim 1 wherein the water immiscible organic solvent contains from 5 to200 g of o-hydroxyaryloxime per liter.
 4. A process as claimed in claim1 wherein the water-immiscible organic solvent is a hydrocarbon.
 5. Aprocess as claimed in claim 4 wherein the hydrocarbon contains little orno aromatic hydrocarbon component.
 6. A process as claimed in claim 1wherein the water-immiscible organic solvent is a halogenatedhydrocarbon.
 7. A process as claimed in claim 1 wherein the aqueousmineral acid is aqueous sulphuric acid.
 8. A process as claimed in claim1 in which the water-immiscible organic solvent phase recovered fromstep (d) is recycled for use in step (a).
 9. A process as claimed inclaim 1 in which the final separated aqueous phase is electrolysed torecover metal therefrom and recycled for use as the aqueous mineral acidin step (c).
 10. A process for extracting copper values from aqueoussolutions of copper salts which comprises the steps of (a) contactingthe aqueous solution with a solution in a water-immiscible, organicsolvent of (1) an o-hydroxyaryloxime which in 0.2 molar solution in analiphatic hydrocarbon solution when loaded with 50% of the theoreticaluptake of copper will be in equilibrium with a 0.1 molar solution ofcopper as copper perchlorate at a pH less than 1 and (2) an alkylphenolcontaining from 3 to 15 alkyl carbon atoms, (b) separating from theaqueous phase the solvent phase containing copper in the form of acomplex with the indicated o-hydroxyaryloxime, (c) contacting thesolvent phase with an aqueous mineral acid, and (d) separating thesolvent phase from the aqueous containing copper in the form of a saltwith the mineral acid, the amount of (2) in said solvent being in therange of 0.1 to 20 times the weight of (1) and such that with the otherconditions used, the overall copper recovery resulting from steps (a) to(d) is greater than when (2) is not included, the pH during thecontacting step (a) being such that the complex which is formed isstable.
 11. A process for extracting copper values from aqueoussolutions of copper salts which comprises (a) contacting the aqueoussolution at pH below 3 with a solution, in a water-immiscible, organicsolvent of (1) an alkyl salicylaldoxime having at least one branchedchain alkyl group containing at least 5 carbon atoms and mixturesthereof, (2) an alkylphenol containing from 3 to 15 alkyl carbon atoms,(b) separating from the aqueous phase the solvent phase containingcopper in the form of a complex with the indicated o-hydroxyaryloxime,(c) contacting the solvent phase with an aqueous mineral acid, and (d)separating the solvent phase from the aqueous phase containing copper inthe form of a salt with the mineral acid, the amount of (2) in saidsolvent being in the range of 0.1 to 20 times the weight of (1) and suchthat with the other conditions used, the overall copper recoveryresulting from steps (a) to (d) is greater than when (2) is notincluded.
 12. A process as set forth in claim 11 in which saidsalicylaldoxime is a mixture of 2-hydroxy-5-nonyl benzaldoximes in whichthe components of the mixture differ in configuration of the branchedchain nonyl group derived by formylation and oximation of mixedp-nonylphenols obtained by condensation of phenol with propylene trimer.13. A process as set forth in claim 11 in which said alkyl phenol is amixture of p-nonyl phenols obtained by alkylation of phenol withpropylene trimer.
 14. A process as set forth in claim 11 in which thewater-immiscible organic solvent contains from 5 to 200 grams of saidsalicylaldoxime and said alkyl phenol in an amount from 0.1 to 20 timesthe weight of said salicylaldoxime.
 15. A process as set forth in claim14 in which the water-immiscible organic solvent contains saidalkylphenol in an amount from 0.1 to 3 times the weight of saidsalicylaldoxime.
 16. A process as set forth in claim 14 in which thewater-immiscible organic solvent contains said alkyl phenol in an amountfrom 2 to 10 times the weight of said salicylaldoxime.
 17. A process asset forth in claim 11 in which said salicylaldoxime is a mixture of5-heptylsalicylaldoximes in which the components of the mixture differin the configuration of the heptyl group derived by formylation andoximation of phenol-heptylene condensate.